A satellite communications system typically includes a constellation of one or more satellites that links ground terminals (e.g., gateway terminals and user terminals). For example, the gateway terminals provide an interface with a network such as the Internet or a public switched telephone network, and each gateway terminal services a number of user terminals located in one or more spot beams. Some architectures permit gateway terminals to service user terminals in their own spot beam coverage area via “loopback” beams. Other architectures permit gateway terminals to service user terminals in other spot beam coverage areas. These and other satellite system architectures tend to have limited flexibility in terms of spectrum utilization, gateway terminal location, and other characteristics.